The debates on laïcité in France have been capped by a claim that French cultural imaginary laïcité has reasserted itself against the ‘new challenge of diversity’, this new challenge explicitly being contrasted to the old challenge of the Catholic Church. There have been plenty of references to the French Third Republic during these debates, yet these references fail to recognise that in fact the concept of diversité was part of the discussions on laïcité during the Third Republic. This is a historical fact that questions the distinction between old and new challenges. This article locates the concept of diversité in the parliamentary deliberations during the making of the ‘Loi du 28 Mars 1882 sur l’enseignement primaire obligatoire’ and the ‘Loi du 9 Décembre 1905 concernant la séparation des églises et de l’État’ and then compares the relations of diversité and laïcité at that time with their relations in contemporary France. The article lays out the move of diversité from a constitutive premise of laïc institutions in the Third Republic to challenging laïcité, and it explores the politics behind this move. I argue that laïcité has not been reasserted but rather has regressed in France.